Mixed-linkage (1.fwdarw.3), (1.fwdarw.4) beta-D-glucans, referred to herein as beta-glucan, are the predominant cell wall components of grain endosperm, particularly oats and barley, and are a well-established antihypercholesterolemic agent. In the case of beta-glucan found naturally in oats, this effect has been acknowledged by the U.S. Food and Drug Administration (FDA). Beta-glucan also has immunostimulatory properties when applied topically to the skin. The biochemical mechanisms by which beta-glucan exerts its therapeutic effects are largely unknown.
Cereal grain seeds generally contain a small amount of beta-glucan, with oats and barley being recognized as the richest sources of this material. The naked oat seed, known in the at as a "groat", typically contains from 2-4% by weight beta-glucan, depending upon oat variety and other factors such as growing conditions. Barley seeds may typically contain twice as much beta-glucan as groats. Beta-glucan is generally found in higher concentrations in the outermost layers of the seed (i.e., the "bran"). Thus, oat bran is defined as containing a minimum of 5.5% by weight beta-glucan, and typically contains up to 6% or 7% by weight beta-glucan.
In order to receive an efficacious amount of beta-glucan for reduction of low density lipoprotein (LDL) and total serum cholesterol, the FDA recommends total beta-glucan ingestion of at least 3 grams daily. However, it is difficult and inconvenient for the average individual to obtain this recommended amount because of the inherently low beta-glucan content in products such as oatmeal, oat bran muffins or cooked barley. For example, in the case of oatmeal, which is simply rolled whole oats, one would have to consume up to 150 grams (dry basis) each day, an amount which most individuals would find extremely burdensome. Accordingly, there is a compelling need to provide a more concentrated form of beta-glucan so that consumers can conveniently ingest therapeutic amounts of this material.
Previous processes for concentrating beta-glucan from cereals such as oats or barley have proven impractical for commercial manufacturing processes because of high cost and/or low yields. The prohibitive cost associated with processes disclosed in the literature is almost always a consequence of reliance upon a precipitation step in which beta-glucan is removed from aqueous solution by an organic solvent, especially alcohols such as ethanol or isopropanol, the use of which entails high in-process losses and difficult reclamation. This is evidenced in the marketplace wherein beta-glucan concentrates are only sold as cosmetic ingredients, with prices typically greater than $100 per pound. There is presently no concentrated form of beta-glucan priced so as to be affordable for use as a dietary supplement or food additive. The most concentrated form of commercially available beta-glucan for nutritional purposes contains just 15% beta-glucan (Nurture.RTM. 1500, supplied by Nurture, Inc., Missoula, Mont.).
U.S. Pat. No. 5,518,710 to Bhatty discloses alkaline extraction of barley and oat bran, addition of an amylolytic agent to degrade starches, followed by precipitation of beta-glucan with a polar alcohol. Beer et al. (Cereal Chemistry 73:9-62, 1996) disclose a process for isolating beta-glucan in which oat bran concentrates are extracted in aqueous solution at alkaline pH, followed by dialysis, ultrafiltration or alcoholic precipitation. The material resulting from these processes had a beta-glucan content of about 60-65%. Westerlund et al. (Carbohydrate Polymers, 20:115-123, 1993) disclose a procedure for isolation of beta-gluen involving lipid extraction, enzymatic removal of starch and protein, and subsequent ethanol precipitation. EP 0 377 530 A2 discloses a process for the preparation of a beta-glucan-cmiched grain for use as a food or food additive, in which oats are slurried in cold water, followed by rapid homogenization and screening of the slurry. U.S. Pat. No. 5,013,561 to Goering et al. discloses a process for recovery of various products, including beta-glucan, from barley. In this process, barley is milled, mixed with water, heated and centrifuged to remove insoluble material. The supernatant is then heated, and centrifuged to remove insoluble material, and the supernatant is subjected to ultrafiltration to remove soluble sugars and to concentrate beta-glucan solids.
There is a need for an entirely aqueous process for concentrating beta-glucan which is efficient, economical and produces highly palatable beta-glucan concentrates for use in foods and pharmaceutical formulations. The present invention addresses this need.